Forbid val field initialization inside EXACLTY_ONCE lambda

unless the lambda is inline. This way, final field will remain final.

compiler/testData/diagnostics/testsWithStdLib/contracts/controlflow/initialization/exactlyOnce/valDefiniteInitialization.kt

@@ -86,7 +86,7 @@ class DefiniteInitializationInInitSection {
     <!MUST_BE_INITIALIZED_OR_BE_ABSTRACT!>val y: Int<!>
 
     init {
-        myRun { x = 42 }
+        myRun { <!CAPTURED_VAL_INITIALIZATION!>x<!> = 42 }
         unknownRun { <!CAPTURED_MEMBER_VAL_INITIALIZATION!>y<!> = 239 }
     }
 }